A Guide to 100 Volt Line Speaker Systems

Low Impedance

For some context, a standard, (low-impedance - 4Ω / 8Ω) audio amplifier such as a Hi-Fi amp takes an input signal from a source device (line level from a CD Player is around 1.2 volts) and makes a copy of it which it then enlarges to an output that usually averages between 5V to 30V, (sometimes higher) depending on its power supply, gain structure design, current handling, and the wattage capability of its components. This output signal is then separated into its separate left and right channel components which are output to their own speaker terminals (Stereo Output).

The output voltage produced is a variable figure that alters with the volume control (which attenuates the input signal level) and is also affected by the amplifier's interaction with the connected low-impedance speakers and cables that present it with resistance, causing it to create either more or less current.

It's basically a fight. An electrical tug-of-war with amp and speakers pushing and pulling within a set of matched (hopefully) boundaries set by the correct impedance and current limitations being respected.

100V Line

A 100-volt line system works differently from this. The initial signal input, preamp stage, and amplification are the same, but after that, it uses a step-up transformer at the output to produce a much higher voltage signal (approx double a standard amp, with a 100V maximum), at a high impedance and low current. This is always a combined mono output, so there is only a single set of terminals.

Because the amplification stage is the same as a 'normal' amp, you will also see a low-impedance output available, but this is provided as a courtesy/problem solver really, and is still a mono feed. You really don't want to use low-impedance speakers on an amp that's primary design is for 100V, so just pretend they aren't there.

This is then paired with 100V specific speakers that feature a step-down transformer to convert this back into a low voltage, low impedance signal they can make use of. It allows the amp to send audio signals far more efficiently over long distances without requiring much current and keeping thermal energy losses small, allowing thinner cable to be used.

This is exactly how the power grid operates, using step-up transformers at the power stations to allow the electricity to be sent over long distances at high voltage with low current, then dropped back to the low voltage and higher current available at your mains power sockets.

• The Amplifier: At the output, the amplified audio signal is stepped up to a much higher voltage than normal (100V max). This increased voltage also raises the output impedance, lowering the required current (Ohms Law), allowing the signal to travel through thinner speaker cables over long distances with minimal resistance and power loss.

  This voltage is also regardless of amplifier power, so a 30W amp will put out 100V max, and a 250W amp will also put out 100V max. The difference between them is the loading capability, allowing the connection of more speakers on a line, or more powerful speakers.

• The Speaker: At each speaker, a small transformer steps down the 100-volt signal to a usable level, converting it back to the low voltage with higher current required to drive a low-impedance speaker. This transformer is usually built into the speaker and often offers a selection of power ‘tappings’, which allow you to set each speaker’s wattage consumption to suit different situations. So a wall speaker for example might have a maximum of 30W output, but could also have tappings at 15W, 7.5W, and 3W.

  This transformer also isolates the speaker’s voice coil impedance, making it ‘invisible’ to the amplifier, which is why you can use multiple speakers on a single cable run with no impedance mismatching or loading issues.

  This also allows for the other unique part of a 100V system, which is that you can simply add the wattage rating (or tapping value) of your speakers together to find the required amplifier power (or vice versa). So for example, if you have 10 speakers that are 10W each, you can use a 100W amplifier. In theory anyway.... In reality, you always want to factor in a good power buffer to account for losses (20-50% ideally!), so in this case with 100W worth of speakers, you would use a 120W or 150W amplifier, and you will find most 100V amps are available in several wattage ratings to make this easy.

Wiring these systems is pretty straightforward, especially compared to low-impedance setups. You can think of it almost as a "plug-and-play" solution.

Because the system uses high voltage and low current, you can run longer cable lengths with thinner, cheaper wire, and multiple speakers can be daisy-chained together from the same amplifier with no issue.

It’s also important to understand that unlike your Hi-Fi which has left and right speaker connections for stereo, a 100V line system operates on full-range mono, so only requires a twin cable (positive and negative) connection to all the speakers.

Stereo is an effect and is only ever used in singular-positioned audio systems where the listener is in equal earshot of both channels. For installations (bars, nightclubs, shopping centres etc) it will always be a mono operation.

You should always use good-quality cable to avoid issues. Ideally, for installation, it will be of a double-insulated type, and a minimum of 2x 0.75mm² to avoid issues, though preferably a bit heavier.

• Amplifier Output: The amplifier will have output terminals labelled as 100V and Common. These are your positive and negative if you prefer, and you connect the speaker cable to these. It may also have low impedance outputs (8Ω etc) but these must not be used. Some 100V line amplifiers allow you to connect to multiple output zones, and if so, each zone will have its own output terminals.

  Though most installs will have all speakers tapped equally, it’s important to understand that each speaker on a line can be tapped differently to suit that area's needs. As long as the total wattage of all speakers connected is within the amplifier's rated output power, it makes no difference.

• Tapping Speakers: Each speaker in a 100V system usually has a power tap option, which will often be a rotary dial on wall speakers, or a choice of input terminals on a ceiling speaker. These allow you to set the maximum power level (in watts) each speaker will draw from the line. You set this based on the speaker’s location, the volume needed in that area, and as a calculated portion of your amplifier's wattage output.

• Daisy-Chain Wiring: This is the standard wiring method and is the most popular. From the amplifier, run a single pair of wires (positive and negative) and connect this to the first speaker's input. From that speaker, you run another cable pair to the next speaker, and so on, daisy-chaining them. It’s about as basic as wiring gets.

  Because of the nature of 100V systems, the number of speakers on a chain is limited more by the amplifier’s power rating than by resistance or cable length, so it’s easy to scale up.

• Central Point Wiring: Also called Star Wiring. This involves separate cable runs to each speaker from the amplifier. This uses more cable but can be a better solution for some installations, especially in multi-room systems.

• Hybrid Wiring: You can also mix the two wiring methods, which is useful for wiring to several zones from a single output amplifier. This becomes particularly useful when adding in-line volume attenuators to specific areas.

  For example, you could have two rooms, each with 4 speakers. Each room can have its speakers wired as a chain, with the start of each chain connected to the amplifiers 100V and Common terminals. What you need to realise with 100V line wiring is the amp doesn't care, as long as you keep the polarity of the wiring correct, and keep to a parallel format.

• Good Wiring Practices: The methods above are given as standard on many different sites and guides, but are actually quite poor for anything larger than a basic single-room installation.

  Professional audio installers will use junction boxes and treat every speaker as a spur in the same way you would do with a lighting circuit or mains wiring. It keeps things neat, makes troubleshooting and upgrades simple, and allows the system to be fully wired and tested while access is available, with speakers being easily connected to the junctions later, usually during final finishing to keep them from being damaged by construction or decorating.

  You can follow our in-depth guide to wiring a 100V system here - How to wire 100V Line Speakers

There are several compelling reasons to opt for a 100-volt line system over a standard low-impedance system, particularly for large spaces and complex installations.

Long Cable Runs Without Signal Loss

In a low impedance system (usually 4Ω, 8Ω, or 16Ω), running long cables results in significant power loss due to the high resistance and impedance of the speakers and cable pulling higher current from the amplifier. Over a distance of more than 15-20 metres, you’ll lose volume and sound quality unless you use significantly thicker cables to compensate, and your amplifier will need to be of good enough quality and power to handle these larger current requirements, which most can't do.

In contrast, 100V systems are designed for long cable runs (even up to thousands of metres) using low-cost, small gauge cable because of the higher voltage and lower current, so the losses are minuscule, and the maximum power draw on the amplifier is pre-determined by adding the selected wattage tappings of the speakers to be connected.

Multiple Speakers on One Amplifier

Due to the resistive loading to its output, the amplifier can only handle a limited number of speakers in a low-impedance setup. You have to carefully calculate the total impedance based on the speaker's ratings, and the wiring method you use, and ensure it doesn't fall outside the amplifier's minimum or maximum rating. This usually means a limit of 2 or 4 speakers, which is obviously no use for a large installation.

With a 100V line system, you don’t need to worry about impedance matching. As long as the total wattage of all speakers being connected is within the amplifier's capacity, you can add as many as you like on the same wiring line. So ignoring our previously discussed 20-50% power buffer for a second, with a 100W amplifier you could for example power 100 speakers tapped at 1W, or 50 speakers at 2W, or 2 speakers tapped at 50W each. The amp doesn't care how you use its power, as long as you don't ask for more than it has to give.

100V Line - Easy System Scaling

If you need to add more speakers to a 100V system, you can just tap into the existing cable and add the new speaker’s with no need to mess around rebalancing the load or worrying about impedance issues. The tappings on extra and existing speakers can be dropped to lower wattage settings if needed, or the amplifier can be upgraded for a more powerful unit without altering the cable installation.

100V Line - Output Power Flexibility

Each speaker’s power tap allows you to adjust its output without needing separate volume controls. This is ideal for spaces where you might need different sound levels. For example, a ceiling speaker in a hallway might only need to be set to 2.5W, while one in a noisy area like a canteen might be set to 10W.

You also have options such as in-line volume attenuators, or a multi-zone amplifier that has separate volume controls to its outputs. These allow for a master volume control of the system from one location, with independent volume adjustment for rooms and areas to suit their use.

100V Line Cost-Effectiveness

Because you can use thinner cables and fewer amplifiers (since a single amplifier can drive dozens or even hundreds of speakers), a 100V system is far more cost-effective than a low-impedance system for large installations. The lower power requirements of installation speakers keep their cost low, and there are no issues with mixing different brands or types of speakers on a single cable run.

Because of their design, 100-Volt systems shine in environments where you need wide coverage and background-level audio. Common places you’ll find these setups include:

• Shopping Centres: Background music and announcements over large areas.
• Offices and Schools: Paging systems and low-level background music.
• Warehouses and Factories: PA systems for announcements across large spaces.
• Outdoor Spaces: Theme parks, car parks, and public areas where sound needs to cover long distances.
• Hospitals: Multi-zone systems for different departments with various volume levels.

100V speakers are available in a wide variety of shapes, sizes, and styles. From standard ceiling speakers and wall-mount speakers to pendant speakers, distribution horn speakers, and garden speakers. You will find ranges that include different woofer sizes, enclosure colours, and weather-resistant designs to suit any installation requirement. The joy of the constant voltage design is that it removes the dreaded impedance issue. This not only allows the use of multiple speakers but also means you can mix and match different types of speakers on a single cable run.

For example, you may have a single daisy chain audio system, using one volume control and playing background music. This chain could feed 6” wall speakers in a room, then some 5” ceiling speakers in a hallway, then outside to some pendants or compact 3” wall speakers. The driver sizes and speaker designs simply do not matter to the amplifier, only that they all have 100V transformers tapped to sit within their wattage capability.

Drawbacks of 100V Line Systems

Of course, no system is perfect, and 100V line systems have some limitations.

• Not Ideal for High-Fidelity Audio: The voltage stepping transformers in both the amplifier and speakers can introduce some signal loss and distortion. This is due to their impedance isolating design which results in some clipping/loss of higher and lower frequencies (bass especially), making these systems less suited for high-fidelity audio applications like home theatre or hi-fi music systems. They’re more about coverage than quality, so while they are perfectly fine for general use, don’t expect audiophile-grade sound.

• Lower Output Power: The individual speakers tend to have lower power ratings, typically 10W or 15W. This is more than enough for background music and announcements, but if you need high-volume or deep bass, low-impedance systems or powered speakers are a better option.

  You will often find entertainment venues employ both types, with a 100V line installation for day-to-day background music and tannoy functions, with a low-impedance PA system for live music or events.